The present invention relates to methods of operating and control systems for refrigeration systems and, more particularly, to methods of operating and control systems for protecting an electric motor driven compressor in a refrigeration system.
Generally, refrigeration systems include an evaporator or cooler, a compressor, and a condenser. Usually, a heat transfer fluid is circulated through tubing in the evaporator thereby forming a heat transfer coil in the evaporator to transfer heat from the heat transfer fluid flowing through the tubing to refrigerant in the evaporator. The heat transfer fluid chilled in the tubing in the evaporator is normally water which is circulated to a remote location to satisfy a refrigeration load. The refrigerant in the evaporator evaporates as it absorbs heat from the water flowing through the tubing in the evaporator, and the compressor operates to extract this refrigerant vapor from the evaporator, to compress this refrigerant vapor, and to discharge the compressed vapor to the condenser. In the condenser, the refrigerant vapor is condensed and delivered back to the evaporator where the refrigeration cycle begins again.
Systems are known for protecting an electric motor driving a compressor in a refrigeration system of the type described above. For example, one such system senses compressor motor current each time the compressor motor is started. If the sensed motor current exceeds a preselected level which could damage the compressor motor, then the refrigeration system is shut down for a period of time before attempting to restart the system. Another such system includes a timing device to provide a time delay for preventing a refrigeration system from starting for a fixed, selected time interval following any de-energization of the compressor motor. This allows refrigerant pressures in the refrigeration system to equalize so that the compressor motor is not started against a high head pressure between the condenser and the evaporator of the refrigeration system which may damage or unduly wear the compressor motor.
While known protection systems, such as those described above, are effective for their intended purposes, these systems are not suitable for protecting an electric motor driven compressor against recycle starts (starts after shutdown of a refrigeration system due to excess capacity) under certain abnormal operating conditions, such as a recycle start under relatively heavy load. However, it is desirable to protect the compressor against recycle starts under such abnormal operating conditions since they may reduce the operating life of the compressor motor and/or the compressor.